Spatial profiling system and method

ABSTRACT

Described herein is a system, a method and a processor-readable medium for spatial profiling. In one arrangement, the described system includes a light source configured to provide outgoing light having at least one time-varying attribute at a selected one of multiple wavelength channels, the at least one time-varying attribute includes either or both of (a) a time-varying intensity profile and (b) a time-varying frequency deviation, a beam director configured to spatially direct the outgoing light into one of multiple directions in two dimensions into an environment having a spatial profile, the one of the multiple directions corresponding to the selected one of the multiple wavelength channels, a light receiver configured to receive at least part of the outgoing light reflected by the environment, and a processing unit configured to determine at least one characteristic associated with the at least one time-varying attribute of the reflected light at the selected one of the multiple wavelengths for estimation of the spatial profile of the environment associated with the corresponding one of the multiple directions.

CLAIM OF PRIORITY

This application is a continuation application and claims the benefit ofpriority of U.S. patent application Ser. No. 16/680,039, filed Nov. 11,2019, which is a continuation application and claims the benefit ofpriority of U.S. patent application Ser. No. 15/277,235, filed Sep. 27,2016, which claims the benefit of priority of Australia PatentApplication No. 2015903943, filed on Sep. 28, 2015, and of AustraliaPatent Application No. 2015904733, filed on Nov. 17, 2015, the benefitof priority of each of which is claimed hereby, and which areincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to a system and method for estimating aspatial profile of an environment.

BACKGROUND OF THE INVENTION

Spatial profiling refers to the three-dimensional mapping of anenvironment as viewed from a desired field of view. Each point or pixelin the field of view is associated with a distance to form athree-dimensional representation of the environment. Spatial profilesmay be useful in identifying objects and/or obstacles in theenvironment, thereby facilitating automation of tasks.

One technique of spatial profiling involves sending light into anenvironment in a specific direction and detecting any light reflectedback from that direction, for example, by a reflecting surface in theenvironment. The reflected light carries relevant information fordetermining the distance to the reflecting surface. The combination ofthe specific direction and the distance forms a point or pixel in thethree-dimensional representation of the environment. The above steps maybe repeated for multiple different directions to form other points orpixels of the three-dimensional representation, thereby estimating thespatial profile of the environment within a desired field of view.

Reference to any prior art in the specification is not, and should notbe taken as, an acknowledgment or any form of suggestion that this priorart forms part of the common general knowledge in any jurisdiction orthat this prior art could reasonably be expected to be understood,regarded as relevant and/or combined with other pieces of prior art by aperson skilled in the art.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a spatialprofiling system including:

a light source configured to provide outgoing light having at least onetime-varying attribute at a selected one of multiple wavelengthchannels, the at least one time-varying attribute includes either orboth of (a) a time-varying intensity profile and (b) a time-varyingfrequency deviation;

a beam director configured to spatially direct the outgoing light intoone of multiple directions in two dimensions into an environment havinga spatial profile, the one of the multiple directions corresponding tothe selected one of the multiple wavelength channels;

a light receiver configured to receive at least part of the outgoinglight reflected by the environment; and

a processing unit configured to determine at least one characteristicassociated with the at least one time-varying attribute of the reflectedlight for estimation of the spatial profile of the environmentassociated with the corresponding one of the multiple directions,

wherein the light receiver is configured to inhibit detection ofnon-reflected light based on a difference in wavelength or modulationbetween the outgoing light and the non-reflected light.

Inhibiting detection of the non-reflected light may include selectingthe selected one of the multiple wavelengths based on a predetermined orrandomised sequence of wavelength channels.

Inhibiting detection of the non-reflected light may includede-correlating the received light from the outgoing light andincoherently mixing the de-correlated light with a sample of theoutgoing light.

Inhibiting detection of the non-reflected light may include performingoptical self-heterodyne of the received light with a sample of theoutgoing light during a time window within which the light source isconfigured to provide the sampled light at the selected one of multiplewavelength channels.

Inhibiting detection of the non-reflected light may include imposing acode modulation on to the time-varying intensity profile of the outgoinglight according to a coding sequence, and wherein the at least onecharacteristic includes an autocorrelation of the reflected light withthe coding sequence. The coding sequence may include a Barker code.Alternatively the code modulation may include a slowly-varying Barkercode and a fast-varying Barker code.

The coding sequence may be adjustable for avoidance of interference withanother spatial mapping system.

The time-varying intensity profile may include periodic modulation at apredetermined frequency. The periodic modulation may include sinusoidalmodulation, and wherein the at least one characteristics may include aphase shift of the sinusoidally modulated reflected light.Alternatively, the periodic modulation includes multiple frequencycomponents, and wherein the at least one characteristics includes atleast one of: (a) a delay of an envelope of a beat tone arising from themultiple frequency components to facilitate a coarser and longer-rangedistance estimation and (b) a phase shift of the periodically modulatedreflected light to facilitate a finer and shorter-range distancedetermination. Alternatively or additionally the time-varying intensitymay profile include a chirped sinusoidal modulation.

In one configuration, the light source is configured to provideadditional outgoing light having the same or a different time-varyingattribute(s) at additionally selected one or more of the multiplewavelength channels in a sequential manner, the beam director isconfigured to direct the additional outgoing light into thecorresponding one or more of the multiple directions in the sequentialmanner, and the processing unit is configured to determine the at leastone characteristic associated with the same or the differenttime-varying attributes of the reflected light at the additionallyselected one or more of the multiple wavelength channel, for estimationof the spatial profile of the environment associated with thecorresponding one or more of the multiple directions.

In this configuration, the sequential manner includes the predeterminedsequence. Alternatively, the sequential manner includes the randomisedsequence.

The beam director may include reversible optics for (a) spatiallydirecting an outgoing collinear beam from the light source into themultiple directions and (b) spatially directing the reflected light inmultiple reversed directions into an incoming collinear beam. Thereversible optics may include a spatially cross-dispersive module. Thespatially cross-dispersive module may include two spatially dispersiveelements in an orthogonal arrangement, each being arranged to steer theoutgoing light into respective one of the two dimensions. The twospatially dispersive elements may include a photonic crystal structure.

The system may further include non-reversible optics for routing theoutgoing light from the light source to the beam director, and forrouting the reflect light from the beam director to the light receiver.The non-reversible optics may include an optical circulator.

The system may further include an optical coupler or beam splitterfollowing the light source

The beam director may include collimating optics for routing reflectedlight collected by bean director to the light receiver along a path notshared by path taken by the outgoing light.

In one configuration, the beam director is one of multiple beamdirectors, each of which is (a) optically coupled to the light sourceand the light receiver, and (b) configured to direct the outgoing lightto a respective environment having a respective spatial profile inresponse to a respective subset of the multiple wavelength channels. Inthis configuration, the beam directors are each fibre-optically coupledto the light source and the light receiver. Alternatively, the lightreceiver is one of multiple light receivers, and the beam directors areeach optically coupled to the light source and the respective one of themultiple light receivers.

The light source may include an etalon module for providingtemperature-related information to the processing unit, and theprocessing unit may be configured to control the light source based onthe temperature-related information.

The beam director may include a cavity for obtainingenvironmental-related information based on intensity of light reflectedfrom the cavity and received by the light receiver.

In one configuration, the time-varying frequency deviation may include alinear change in optical frequency. The time-varying frequency deviationmay include a sawtooth or triangular waveform. The processing unit maybe further configured to determine at least another characteristic ofthe reflected light for estimation of a speed of a target in theenvironment.

According to a second aspect of the invention there is provided aspatial profiling method including the steps of:

providing, by a light source, outgoing light having at least onetime-varying attribute at a selected one of multiple wavelengthchannels, the at least one time-varying attribute includes either orboth of (a) a time-varying intensity profile and (b) a time-varyingfrequency deviation;

spatially directing, by a beam director, the outgoing light into one ofmultiple directions in two dimensions into an environment having aspatial profile, the one of the multiple directions corresponding to theselected one of the multiple wavelength channels;

receiving, by a light receiver, at least part of the outgoing lightreflected by the environment; and

determining, by the processing unit, at least one characteristicassociated with the at least one time-varying attribute of the reflectedlight for estimation of the spatial profile of the environmentassociated with the corresponding one of the multiple directions,

wherein the light receiver is configured to inhibit detection ofnon-reflected light based on a difference in wavelength or modulationbetween the outgoing light and the non-reflected light.

According to a third aspect of the invention there is provided aprocessor-readable medium including instructions, which when executed bya processing unit in a spatial profiling system, cause the system to:

-   -   provide, by a light source, outgoing light having at least one        time-varying attribute at a selected one of multiple wavelength        channels, the outgoing light being spatially directed by a beam        director into one of multiple directions in two dimensions into        an environment having a spatial profile, the at least one        time-varying attribute includes either or both of (a) a        time-varying intensity profile and (b) a time-varying frequency        deviation, the one of the multiple directions corresponding to        the selected one of the multiple wavelength channels; and    -   determine, by the processing unit, at least one characteristic        associated with the at least one time-varying attribute of at        least part of the outgoing light reflected by the environment        and received by a light receiver for estimation of the spatial        profile of the environment associated with the corresponding one        of the multiple directions,

wherein the light receiver is configured to inhibit detection ofnon-reflected light based on a difference in wavelength or modulationbetween the outgoing light and the non-reflected light.

Further aspects of the present invention and further embodiments of theaspects described in the preceding paragraphs will become apparent fromthe following description, given by way of example and with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C each illustrate an arrangement of a spatialprofiling system.

FIGS. 2A and 2B each illustrate an arrangement of a light sourceproviding outgoing light having a time-varying intensity profile.

FIGS. 2C and 2D each illustrate an arrangement of a light sourceproviding outgoing light having a time-varying frequency deviation.

FIG. 3A illustrates an arrangement of a beam director of the spatialprofiling system.

FIG. 3B illustrates schematically an association between pixels of afield of view and wavelength channels of emitted light of the lightsource.

FIG. 4A illustrates an arrangement of timing control of lighttransmission windows and the light receiving windows.

FIG. 4B illustrates an example of the outgoing light intensity over timeover the light transmission and receiving windows.

FIGS. 4C and 4D each illustrate an example of periodic modulation.

FIGS. 4E and 4F each illustrate an example of code modulation.

FIGS. 5A and 5B illustrate a comparison between arrangements without andwith time-varying frequency deviation control, respectively.

FIG. 6A illustrates the optical frequency of local light, opticalfrequency of received light and their frequency difference in the casewhere a target is stationary.

FIG. 6B illustrates the optical frequency of local light, opticalfrequency of received light and their frequency difference in the casewhere a target is moving.

DETAILED DESCRIPTION OF EMBODIMENTS

In this specification, “intensity” means optical intensity and, unlessotherwise stated, is interchangeable with “optical power”.

Described herein is a spatial profiling system. The described systemprovides an estimation of the spatial profile of an environment as seenfrom one or more particular perspectives, by determining the distance ofany reflecting surface, such as that of an object or obstacle, within asolid angle or field of view for each perspective. The described systemmay be useful in monitoring relative movements or changes in theenvironment.

For example, in the field of autonomous vehicles (land, air, water, orspace), the described system can estimate from the vehicle's perspectivea spatial profile of the traffic conditions, including the distance ofany objects, such as an obstacle or a target ahead. As the vehiclemoves, the spatial profile as viewed from the vehicle at anotherlocation may change and may be re-estimated. As another example, in thefield of docking, the described system can estimate from a containership's perspective a spatial profile of the dock, such as the closenessof the container ship to particular parts of the dock, to facilitatesuccessful docking without collision with any parts of the dock. As yetanother example, in the field of line-of-sight communication, such asfree-space optical or microwave communication, the described system maybe used for alignment purposes. Where the transceiver has moved or ismoving, it may be continuously tracked so as to align the optical ormicrowave beam.

As further examples, the applicable fields include, but are not limitedto, industrial measurements and automation, site surveying, military,safety monitoring and surveillance, robotics and machine vision,printing, projectors, illumination, attacking and/or flooding and/orjamming other laser and IR vision systems

FIG. 1A illustrates an arrangement of a spatial profiling system 100Aaccording to the present disclosure. The system 100A includes a lightsource 102, a beam director 103, a light receiver 104 and a processingunit 105. In the arrangement of FIG. 1 , outgoing light from the lightsource 102 is directed by the beam director 103 in a direction in twodimensions into an environment 110 having a spatial profile. If theoutgoing light hits an object or a reflecting surface, at least part ofthe outgoing light may be reflected (represented in solid arrows), e.g.scattered, by the object or reflecting surface back to the beam director103 and received at the light receiver 104. The processing unit 105 isoperatively coupled to the light source 102 for controlling itsoperations. The processing unit 105 is also operatively coupled to thelight receiver 104 for determining the distance to the reflectingsurface, by determining the round-trip distance travelled by thereflected light.

The light source 102, the beam director 103, the light receiver 104 maybe optically coupled to one another via free-space optics, and/oroptical waveguides such as optical fibres or optical circuits in theform of 2D or 3D waveguides. As described further below, outgoing lightfrom the light source 102 is provided to the beam director 103 fordirecting into the environment. Any reflected light collected by thebeam director 103 may be directed to the light receiver 104. In onearrangement, light from the light source 102 is also provided to thelight receiver 104 for optical processing purposes via a direct lightpath (not shown) from the light source 102 to the light receiver 104.For example, the light from the light source 102 may first enter asampler (e.g. a 90/10 fibre-optic coupler), where a majority portion(e.g. 90%) of the light is provided to the beam director 103 and theremaining sample portion (e.g. 10%) of the light is provided to thelight receiver 104 via the direct path. In another example, the lightfrom the light source 102 may first enter an input port of an opticalswitch and exit from one of two output ports, where one output portdirects the light to the beam director 103 and the other output portre-directs the light to the light receiver 104 at a time determined bythe processing unit 105. The light receiver 104 is configured to inhibitdetection of non-reflected light based on a difference in wavelength ormodulation between the outgoing light and the non-reflected light.Non-reflected light includes light that does not arise from thereflection of the outgoing light, and hence should not assist theprocessing unit 105 in determining the distance of the reflectingsurface. This inhibition is intended to address issues such as falsedetection and security. As will be apparent from the remainder of thedescription, there are a number of ways to inhibit detection of thenon-reflected light, such as including one or more of the following:

-   -   selecting a wavelength channel based on a predetermined or        randomised sequence of wavelength channels;    -   de-correlating the received light from the outgoing light and        incoherently mixing the de-correlated light with a sample of the        outgoing light;    -   performing optical self-heterodyne of the received light with a        sample of the outgoing light at a specific time window;    -   imposing a time-varying intensity modulation profile having a        specific frequency on the outgoing light;    -   imposing a time-varying frequency deviation or intensity profile        having a specific frequency chirp characteristic (e.g. a        specific chirp rate) on the outgoing light; and    -   imposing a code modulation having a specific coding sequence on        to the outgoing light.

In one example, the light source 102, the beam director 103, the lightreceiver 104 and the processing unit 105 are substantially collocated.For instance, in an autonomous vehicle application, the collocationallows these components to be compactly packaged within the confines ofthe vehicle or in a single housing. In another example, in a spatialprofiling system 100B as illustrated FIG. 1B, the light source 102, thelight receiver 104 and the processing unit 105 are substantiallycollocated within a “central” unit 101, whereas the beam director 103 isremote from the central unit 101. In this example, the central unit 101is optically coupled to the remote beam director 103 via one or moreoptical fibres 106. This example allows the remote beam director 103,which may include only passive components (such as passivecross-dispersive optics), to be placed in more harsh environment,because it is less susceptible to external impairments such as heat,moisture, corrosion or physical damage. In yet another example, asillustrated in FIG. 1C, a spatial profiling system 100C may include asingle central unit 101 and multiple beam directors (such as 130A, 130Band 130C). Each of the multiple beam directors may be optically coupledto the central unit 101 via respective optical fibres (such as 106A,106B and 106C). In the example of FIG. 1C, the multiple beam directorsmay be placed at different locations and/or orientated with differentfields of view.

Light Source

A light wave involves an oscillating field E which can mathematically bedescribed as:

${{E(t)} \propto {\sqrt{I(t)}{\cos\left\lbrack {\varphi(t)} \right\rbrack}}} = {\sqrt{I(t)}{\cos\left\lbrack {{\frac{2\pi c}{\lambda_{k}}t} + {2\pi{f_{d}(t)}t}} \right\rbrack}}$

where I(t) represents the intensity of the light,φ(t)=(2πc/λ_(k))t+2πf_(d)(t)t represents the phase of the field, λ_(k)represents the centre wavelength of the k-th wavelength channel, f_(d)(t) represents the optical frequency deviation (hereinafter “frequencydeviation” for simplicity) from the centre optical frequency of the k-thwavelength channel, and c=2.998×10⁸ m/s is the speed of light. The lightsource 102 is configured to provide the outgoing light having at leastone time-varying attribute, such as a time-varying intensity profileI(t) and/or a time-varying frequency deviation f_(d)(t).

Light having the at least one time-varying attribute may be directedinto the environment, back-reflected by a reflecting surface, andcollected by the system 100A. As will be described further below, theprocessing unit 105 may be configured determine the round-trip time, andhence round-trip distance, of the back-reflected light by determining atleast one characteristic associated with the at least one time-varyingattribute of the back-reflected light.

(a) Time-Varying Intensity Profile I(t)

In one arrangement, the light source 102 is configured to provide theoutgoing light having a time-varying intensity profile I(t) at aselected one of multiple wavelength channels (each represented by itsrespective centre wavelength λ₁, λ₂, . . . λ_(N)). FIG. 2A illustratesan example of one such arrangement of the light source 102. In thisexample, the light source 102 may include a wavelength-tunable laser 202of substantially continuous-wave (CW) light intensity, such as awavelength-tunable laser diode, providing light of a tunable wavelengthbased on one or more electrical currents (e.g. the injection currentinto the into one of more wavelength tuning elements in the lasercavity) applied to the laser diode. In another example, the light source102 may include a broadband light source and a tunable spectral filterto provide substantially continuous-wave (CW) light intensity at theselected wavelength.

In the example of FIG. 2A, the light source 102 may include a modulator204 for imparting a time-varying intensity profile on the outgoinglight. In one example, the modulator 204 is a semiconductor opticalamplifier (SOA) integrated on the laser diode. The electrical currentapplied to the SOA may be varied over time to vary the amplification ofthe CW light produced by the laser over time, which in turn provideoutgoing light with a time-varying intensity profile. In anotherexample, the modulator 204 is an external modulator (such as a MachZehnder modulator or an external SOA modulator) to the laser diode. Inanother arrangement, as illustrated in FIG. 2B, instead of having awavelength-tunable laser 202, the light source 206 includes a broadbandlaser 208 followed by a wavelength-tunable filter 210.

(b) Time-Varying Frequency Deviation f_(d)(t)

In another arrangement, the light source 102 is configured to providethe outgoing light having a time-varying frequency deviation f_(d) (t)at a selected one of multiple wavelength channels (λ₁, λ₂, . . . λ_(N)).FIG. 2C illustrates an example of one such arrangement of the lightsource 102.

The instantaneous optical frequency f and the instantaneous wavelength λof a light field represent an equivalent physical attribute of awave—the oscillation rate of the light field—and are related by the waveequation c=fλ. Since the speed of light c is a constant, varying eitherf or λ necessarily varies the other quantity accordingly. Similarly,varying either λ_(k) or f_(d) may be described as varying the otherquantity accordingly. In particular, f_(d) (t) and λ_(k) are related asfollows:λ=c/(c/λ _(k) +f _(d)) andf=c/λk+f _(d)

In practice, changes in f_(d)(t) and λ_(k) of the light source 102 maybe effected by a single control, e.g. tuning the wavelength of the lightsource 102 by, for example, an injection current into a laser diode.However, for clarity, the description hereinafter associates frequencydeviation f_(d) (t) with deviation in the optical frequency within asingle wavelength channel from its centre optical frequency, whereaschanges in λ_(k) are associated with causing the light source 102 tojump from one wavelength channel to another. For example, a smaller andsubstantially continuous wavelength change of the light source 102 isdescribed to cause a time-varying frequency deviation f_(d)(t), whereasa larger and stepped wavelength change of the light source 102 isdescribed to cause the light source 102 to jump from wavelength channelλ_(k) to λ_(k+1).

In the example of FIG. 2C, the light source 102 may include awavelength-tunable laser 202 of substantially continuous-wave (CW) lightintensity, such as a wavelength-tunable laser diode, providing light ofa tunable wavelength based on one or more electrical currents (e.g. theinjection current into the into one or more wavelength tuning elementsin the laser cavity) applied to the laser diode. In another example, thelight source 102 may include a broadband light source and awavelength-tunable spectral filter to provide substantiallycontinuous-wave (CW) light intensity at the selected wavelength.

(c) Time-Varying Intensity Profile I(t) and Frequency Deviation f_(d)(t)

In another arrangement, the light source 102 may be configured toprovide outgoing light with both time-varying intensity profile I(t) andtime-varying frequency deviation f_(d)(t). The examples shown in FIGS.2A and 2B are both suitable for use in such an arrangement of the lightsource 102. The description above on (a) time-varying intensity profileI(t) and (b) time-varying frequency deviation f_(d) (t) applies to suchan arrangement of the light source 102.

The operation of the light source 102, such as both thewavelength-tunable laser 202 (e.g. its wavelength) and the modulator 204(e.g. the modulating waveform), may be controlled by the processing unit105, which is described further below.

Beam Director

The beam director 103 is configured to spatially direct the outgoinglight into one of multiple directions (301-1, 301-2, . . . 301-N) in twodimensions into the environment 110. The direction into which theoutgoing light is directed corresponds to, or is based on, the selectedone of the multiple wavelength channels (centred at λ₁, λ₂, . . .λ_(N)). For arrangements where the outgoing light has a time-varyingfrequency deviation f_(d) (t) within a selected wavelength channel, theselected wavelength channel may encompass a set of closely spacedwavelengths resulting from the time-varying frequency deviation f_(d)(t) within that wavelength channel. For simplicity, in sucharrangements, although the exact wavelength varies slightly over time,the description below uses the notation λ_(k) (i.e. λ₁, λ₂, . . . λ_(N))to, unless otherwise stated, represent the wavelength channel and,collectively, the set of closely spaced wavelengths.

FIG. 3A illustrates an arrangement of the beam director 103, whichincludes spatially cross-dispersive optics, such as passive (i.e.non-moving) spatially cross-dispersive optics. In this arrangement, thepassive spatially cross-dispersive optics includes a combination of twospatially dispersive elements optically coupled or arranged in anorthogonal manner. For example, a first spatially dispersive element 302may be an echelle grating, a virtually imaged phased array (VIPA), and asecond spatially dispersive element 303 may be a grating, or prism orgrism. The first spatially dispersive element 302 is oriented with thesecond spatially dispersive element 303 such that light from the lightsource 102 is steered across a first spatial dimension (e.g. along thehorizontal direction or X axis) by the first spatially dispersiveelement 302 and across a second, orthogonal, spatial dimension (e.g.along the vertical direction or Y axis) by the second spatiallydispersive element 303. This arrangement results in a two-dimensionalbeam steering by folding a one-dimensional beam steering into differentdiffraction orders to cover the second spatial dimension. An advantageof using passive cross-dispersing optics is that they allow anall-solid-state system with no moving parts and hence a tendency oflower failures, leading to the possibility to miniaturize the systempotentially achieving high reliability, high durability, low powerconsumption and making it suitable for large-scale manufacturing. Inanother arrangement, the first spatially dispersive element 303 and/orsecond spatially dispersive element 303 may be replaced by a opticalwaveguide, such as a 3D optical waveguide, or a photonic crystalstructure, such as a 3D photonic crystal. In yet another arrangement,both spatially dispersive elements 302 and 303 may be replaced by aphotonic crystal structure.

Although not shown, an alternative arrangement of the combination oflight source and beam director is an array of wavelength-tunable lightemitters, each associated with a corresponding spatially dispersiveelement. The light emitter array is configured to emit and spread lightalong one dimension (e.g. along the horizontal direction to the X-axis),whereas each spatially dispersive element is configured to disperselight from the corresponding light emitter along a substantiallyperpendicular dimension (e.g. along the vertical direction to theY-axis), resulting in light being directed in two dimensions into theenvironment. In one configuration, the wavelength-tunable light emittersare an array of individually wavelength-tunable lasers. In anotherconfiguration, the wavelength-tunable light emitters are a single lasercoupled to an array of SOAs. If multiple SOAs are used, the multipleSOAs may be separately coded (see description on code modulation furtherbelow) for identifying light emitted from a particular SOA in the array.The spatially dispersive element may be a grating, for example.

As mentioned above, in some arrangements, the outgoing light has atime-varying frequency deviation f_(d)(t), where the instantaneousoptical frequency deviates from the centre optical frequency of the k-thwavelength channel. In these arrangements, the instantaneous wavelengthat each selected wavelength channel is also varied slightly. As will beexplained further below in relation to FIG. 3B, such a time-varyingfrequency deviation manifests as a small movement in the direction ofthe outgoing light.

In the above arrangements, the beam director 103 includes reversibleoptics for spatially directing an outgoing collinear beam from the lightsource 102 into the multiple directions. Further, the reversible opticsspatially directs any reflected light in reversed directions into anincoming collinear beam. The first and second spatially dispersiveelements 302 and 303 may act as such reversible optics. The incomingcollinear beam means that optics required for the light receiver 104 issimplified since reflected light shares at least part of the opticalpath taken by the outgoing light within the beam director 103.Furthermore, the reversible optics enhances security of the system bysuppressing any spoofed light signal from a direction that does notalign with the direction of the outgoing light. Still furthermore, thereversible optics suppresses collection of light reflected via multiplepaths or trajectories, where any reflected light collected innon-reversed directions of the outgoing light would otherwise result inan incorrect distance measurement.

In an alternative arrangement, the beam director 103 includescollimating optics (not shown) to collect reflected light. Thecollimating optics may be separate from the reversible andnon-reversible optics, such that any light collected by the collimatingoptics may be routed to the light receiver 104 along a path not sharedby path taken by the outgoing light within the beam director 103. In oneexample, the collimating optics includes a large aperture lens, an anglemagnifier or a fish eye lens for a widened field of view, oralternatively non imaging optics like compound parabolic concentrators.

In the arrangement of FIG. 3A, the beam director 103 also includesnon-reversible optics. In one example, the non-reversible opticsincludes an optical circulator 304. The circulator 304 routes outgoinglight to be passed from the light source 102 to the environment 110 viathe beam director 103, and routes any light reflected back from theenvironment 110 collected into the beam director 103 to be passed to thelight receiver 104. In an alternative example (not shown), thenon-reversible optics includes a beam splitter instead of an opticalcirculator. In yet another alternative example (not shown), thenon-reversible optics includes an optical coupler, such as a 2×1 or 2×2fibre-optic coupler, for coupling light provided by the light source 102from one port in a forward direction as outgoing light, and for couplingreflected light collected by the beam director 103 to another port intoa backward direction.

Although the description herein is focussed on a directing light in twodimensions into the environment, there may be scenarios where light isdirected in only one dimension into the environment. Beam direction inone dimension relaxes the power requirements as well as the field ofview requirements compared to a two-dimensional case. A skilled personwould appreciate that the description herein on the beam director isstill applicable to such scenarios with minor modifications. Forexample, as a modification to the beam director 103, the secondspatially dispersive element 303 may be omitted, with the firstspatially dispersive element 302 remaining to direct light into the onedimension only based on the wavelength of the light source 104. In thisexample, the spatially dispersive element 302 may be a compound prism,or grating or grism. The reflected light may be collected via reversibleoptics or collimating optics. Where collimating optics are used, thecollimating optics may include a compound prism for collimating thespatially dispersed light into collimated light for providing to thelight receiver 104.

Light Receiver

The light receiver 104 is configured to receive at least part of theoutgoing light reflected by the environment. The light receiver 104includes an optical-to-electrical conversion unit to convert an opticalsignal into an electrical signal. In one arrangement, theoptical-to-electrical conversion unit includes a photodetector, whichproduces a photocurrent whose magnitude varies over time based on thetime-variation of the intensity of a received optical signal. In anotherarrangement, the optical-to-electrical conversion unit includes anoptical signal processing unit, such as an optical self-heterodynedetector, which nonlinearly mixes any received light with a locallyoscillated signal (i.e. local light from the light source 102) toproduce an electrical signal that is responsive to difference in opticalfrequency (or, equivalently, wavelength) between the local light and thereceived light. The resulting electrical signal has improvedsignal-to-noise ratio for a received wavelength at or close to the localwavelength while suppressing electrical signals caused by wavelengthsfar from the local wavelength due to the inherently limited electronicbandwidth of the detector. Since the reflected light need not becoherent, speckles are reduced. In one example, the opticalself-heterodyne detector may be a photodiode, which is a photodetectorthat provides the required non-linear mixing of the locally oscillatorsignal and the received light.

In an example implementing optical self-heterodyne detection, thereceived light and the locally oscillated signal may be de-correlated bya differential optical path length to the optical self-heterodynedetector, such that the optical self-heterodyne detection issufficiently incoherent for controllably reducing any speckles. Thedifferential path length required for substantially speckle-freeoperation depends on coherence length of the light source 102. In thecase where the light source 102 is a semiconductor laser, which has arelatively short coherence length, approximately 30 metres of opticalfibre is expected to be required. In comparison, where the light source102 is a narrow-linewidth laser, which has a relatively long coherencelength, approximately 1 kilometre of optical fibre is expected to berequired.

In either arrangement, the resulting electrical signal may be processedby the processing unit 105 for determining the round-trip distancetravelled by of the reflected light. Depending on the attribute(s) ofthe outgoing light being varied over time, a different characteristic(s)associated with the time-varying attribute(s) is (are) detected todetermine at least the round-trip distance, as further described below.

The required response time of the photodetector depends on the timescale of intensity variation imparted on the outgoing light. It isenvisaged that the present technique requires a modulation bandwidth of100 MHz or less, hence requiring a photodetector having a bandwidth ofapproximately 60-80 MHz (or a response time in the order of 15-20 ns).

Processing Unit

As mentioned above, the processing unit 105 is operatively coupled tothe light source 102 for controlling its operations and, alsooperatively coupled to the light receiver 104 for determining theround-trip distance travelled by the reflected light and hence thedistance of the object. In the arrangement of FIG. 2A or 2C, theprocessing unit 105 controls the tunable wavelength of the light source102 by, for example, controlling the one or more currents (e.g. theinjection current into the gain medium, or temperature-controllingcurrent into the heatsink) applied to the laser diode. This wavelengthcontrol allows control over both the wavelength channel λ_(k) fordirecting the outgoing light by the beam director 103 based onwavelength, as well as any time-varying frequency deviation f_(d) (t)within a wavelength channel.

Further, the processing unit 105 controls the time-varying intensityprofile by, for example, controlling the current applied to themodulator 204 (which as mentioned can be an SOA or a Mach-Zehnderexternal modulator). The time-varying intensity profile can take one ormore of several forms, each requiring a corresponding detection methodfor determining the distance of the object. The processing unit 105 mayinclude a processor-readable medium including instructions for thedescribed functions. The processing unit 105 may be implemented as anyone or more of a microprocessor, a field-programmable gate array (FPGA)and an application-specific integrated circuit (ASIC).

Wavelength Control

Controlling the wavelength channel λ_(k) of light from the light source102 effectively controls the direction (in two dimensions) in which thebeam director 103 directs the light to the environment 110. Eachwavelength channel represents a pixel or a point within a field of view,as schematically shown in FIG. 3B, which illustrates 100 pixels orpoints represented in a Cartesian-based coordinate system, with 10pixels across each of X and Y directions. In the arrangement where thebeam director 103 includes two spatially dispersive elements, the firstand second spatially dispersive elements may be configured to spatiallydisperse light in the X and Y directions, respectively, based on thewavelength channel. To generate a spatial profile, each wavelength (andhence each direction, pixel or point) may be associated with a distancefrom a reflecting surface in that direction, pixel or point.Additionally, controlling the wavelength of light within a wavelengthchannel provides the outgoing light a time-varying frequency deviationf_(d)(t). As mentioned, changes wavelength channel λ_(k) are associatedwith larger and stepped changes in wavelength (or optical frequency),whereas the time-varying frequency deviation f_(d) (t) is associatedwith smaller and substantially continuous changes in wavelength (oroptical frequency).

If the light source 102 is a telecommunication-grade laser, it may havea wavelength tuning range of up to 40 nm, for example from approximately1527 nm to approximately 1567 nm, and an optical frequency tuningresolution of approximately 10 MHz (which at 1550 nm corresponds to awavelength tuning resolution of approximately 0.0001 nm). As anillustrative example, consider that two neighbouring wavelength channelswhose centre wavelengths λ_(k) and λ_(k+1) are 1550.00 nm and 1550.10nm, respectively, corresponding to centre optical frequencies of193.419355 THz and 193.406877 THz, respectively. The two wavelengthchannels may be associated with two neighbouring pixels in FIG. 3B. Inthis example, the two wavelength channels have an optical frequencydifference of 12.478 GHz. In contrast, the frequency deviation of thelight source 102 may be caused to vary over time within the samewavelength channel within a range of approximately +/−0.5 GHz. In otherwords, in this example, while more than 10 GHz of optical frequencychange is required to direct the outgoing light beam from one pixel tothe next (i.e. the width of one pixel), a maximum frequency deviation ofapproximately +/−0.5 GHz causes the outgoing light beam to move lessthan +/−5% of the pixel width. This slight movement of the light beamdue to the time-varying frequency deviation f_(d) (t) may manifest as anoise-averaging or smoothing effect on the spatial profile measurement.

In the example of FIG. 1C, where the system 100C includes multiple beamdirectors, each beam directors may be configured to be responsive to adifferent range of wavelength channels. For example, light of wavelengthchannels centred at λ₁, λ₂, . . . λ_(N) routed to beam director 103A maybe directed to its related environment and back reflected to reach lightreceiver 104, whereas light of the same wavelength channels routed tobeam directors 103B and 103C may be directed not to their respectiveenvironments (e.g. instead to a light absorber) to suppress anyreflected light reaching light receiver 104.

Timing Control

The processing unit 105 controls the respective timing of lighttransmission windows (such as 401 and 403) and the light receivingwindows (such as 402 and 404). FIG. 4A illustrates one such arrangementof timing control from the perspective of the system as a whole (seebelow for the perspectives of the light source 102, the beam director103 and the light receiver 104). In this arrangement, light of differentwavelength channels is provided in a sequential manner. The processingunit 105 generally alternates between light transmission windows ofdifferent wavelength channels λ₁, λ₂, . . . λ_(N) with light receivingwindows of respective wavelength channels λ₁, λ₂, . . . λ_(N). Inanother arrangement, there may be an overlap between neighbouringtransmission and receiving windows. For example, the transmission andreceiving windows for a particular wavelength channel may start and endat the same time. As another example, the transmission and receivingwindows for a particular wavelength channel may start at the same time,but the transmission windows ends earlier than the receiving windowends. In yet another arrangement, there may be no overlap betweenneighbouring transmission and receiving windows.

During the light transmission window 401, the processing unit 105 causesthe light source 102 to produce light at a first wavelength channel λ₁).For example, the processing unit 105 may cause a specific currentcorresponding to wavelength λ₁ to be applied to the laser diode.

During the light receiving window 402, light from the light source 102may cease to be produced. Alternatively, the light source 102 continuesto produce light redirected to the light receiver 104 via the directpath for the optical switch. Still alternatively, in the example with asampler following the light source 102, where a portion of the outgoinglight is provided to the light receiver 104, the light source 102continues to produce light but re-direction is necessary. The processingunit 105 detects any electrical signal corresponding to any lightreceived by the light receiver 104. If optical self-heterodyne detectionwith the local oscillating signal from the light transmission window 401is used, then received light at wavelengths other than those of thefirst wavelength channel λ₁ will likely be suppressed due to theinherently limited detector bandwidth. Such suppression enhances thesecurity of the system by minimising the impact of spoofing by, e.g.optical flooding. The use of optical self-heterodyne also has a benefitthat, if the light source 102 is a semiconductor laser, any undesiredside modes of the semiconductor laser are also filtered out. During thelight receiving window 402, light at the first wavelength channel λ₁from the light source 102 may be either ceased to be provided orredirected, e.g. via an optical fibre, to the light receiver 104 formixing in optical self-heterodyne detection. The description on thelight transmission window 401 and the light receiving window 402 issimilarly applicable to the light transmission window 403 and the lightreceiving window 404, respectively, with a change of wavelength channelλ₁ to wavelength channel λ₂. The windows (such as 401, 402, 403 and 404)may be of the same or different duration.

To facilitate one arrangement of timing control by the processing unit105, the light source 102, the beam director 103 and the light receiver104 may function as follows in an illustrative example. In this example,a sampled portion of the light from the light source 102 is provided tothe light receiver for optical self-heterodyne detection, and the lightsource 102 does not cease to produce light during a receiving window:

-   -   The processing unit 105 controls the light source 102 to produce        a sequence of light transmission windows each associated with a        different wavelength channel (e.g. λ₁, λ₂ . . . λ_(N)). The        light source 102 produces light continuously or substantially        continuously, as it is tuned to another wavelength channel        without being switched off.    -   The beam director 103 is provided with light at wavelength        channel λ₁ and directs it into direction 1. While light at        wavelength channel λ₁ is still being directed into direction 1,        reflected light at wavelength channel λ₁ may be collected by the        beam director 103. As the processing unit 105 controls the light        source 102 to change to wavelength channel λ₂, the beam director        103 is provided with light at λ₂ and directs it into direction        2. While light at wavelength channel λ₂ is still being directed        into direction 2, reflected light at wavelength channel λ₂ may        be collected by the beam director 103, and so on for subsequent        wavelength channels.    -   The light receiver 104 receives a sample portion of the outgoing        light from the light source 102 while the light source 102 emits        light. For example, while the light receiver 104 is provided        with sampled outgoing light at wavelength channel λ₁, the light        receiver may also receive reflected light at wavelength channel        λ₁ which mixes with the sampled outgoing light at wavelength        channel λ₁ for optical self-heterodyne detection. As the        processing unit 105 controls the light source 102 to change to        wavelength channel λ₂, the light receiver 104 is provided with        sampled outgoing light at λ₂, while still potentially receiving        light at wavelength channel λ₁. While the light receiver 104 is        being provided with sampled outgoing light at wavelength channel        λ₂, the light receiver may also receive reflected light at        wavelength channel λ₂ which mixes with the sampled outgoing        light at wavelength channel λ₂ for optical self-heterodyne        detection, and so on for subsequent wavelengths.    -   At the times where the light receiver 104 is subject to sampled        outgoing light and reflected light at mismatched wavelength        channels, the resulting electrical signal is expected to have a        sufficiently high beat frequency which can be filtered out via        electronic or digital signal processing. Further, for mismatch        where the beat frequency is higher than the bandwidth of the        optical processing unit (e.g. the photodiode), no dedicated        filtering is required due to the limited frequency response of        the optical processing unit.

Other arrangement of timing controls may also be possible. For example,light from the light source 102 may be re-directed via a direct path,other than sampled, to the light receiver 104.

The processing unit 105 may be configured to control the sequentialmanner in a predetermined sequence, such as in a wavelength-increasingor wavelength-decreasing order, effectively performing a 2D raster scanof the field of view. To enhance security, the predetermined sequencemay hop across different wavelength channels in a manner only known tothe system (e.g. λ₁, λ₁₀₀, λ₃₅, λ₁₅₀, . . . ).

The predetermined sequence may also be adjusted by the processing unit105, for example, if it is desired to look at a selected portion of thefield of view. Referring to FIG. 3B, the system may be a normal “scan”mode, in which the processing unit 105 is configured that thepredetermined sequence is λ₁, λ₂, . . . λ₁₀₀ covering a particular fieldof view. If the processing unit 105 determines that most of the 100pixels are associated with a distance of around 300 metres (e.g,indicating a wall at 300 metres away), except that 4 neighbouring pixelsat λ₁₂, λ₁₃, λ₂₂, λ₂₃ are associated with a distance of around 50metres, then the processing unit 105 may determine that there is anobject around 50 metres away in the direction of the 4 neighbouringpixels.

After determining that there is an object around 50 metres away in thedirection of the 4 neighbouring pixels, in one arrangement, the systemmay enter a “stare” mode, in which the processing unit 105 may beconfigured to adjust the predetermined sequence to λ₁₂, λ13, λ₂₂, andλ₂₃ (i.e. 2×2 pixels) only, covering the direction of the 4 neighbouringpixels only to determine any changes in distance of that object overtime. Any changes in distance would indicate movement close to or awayfrom the system. In another arrangement, the system may enter a “track”mode, in which the processing unit 105 may be configured to determinethe distance associated with the 4 neighbouring pixels as well assurrounding pixels to anticipate any movement of the object outside thestared field of view. For example, the processing unit 105 may beconfigured to adjust the predetermined sequence to λ1, λ₂, λ₃, λ₄, λ₁₁,λ₁₂, λ₁₃, λ₁₄, λ₂₁, λ₂₂, λ₂₃, λ₂₄, λ₃₁, λ₃₂, λ₃₃, and λ₃₄ (i.e. 4×4pixels).

The processing unit 105 may also be configured to adjust the frame rateby controlling how quickly the light source 102 is tuned from onewavelength channel to the next, and the spatial resolution by tuning to,for example, every second wavelength channel (i.e. λ₁, λ₃, λ₅, λ₇ . . .) of all the tunable wavelength channels of the light source 102. Therefreshing rate for completing a full scan (i.e. determining a distanceassociated with all desired wavelengths) depends on the desired numberof directions, pixels or points within a field of view, and the durationof the light transmission and receiving windows. The refreshing rate maybe different for different applications. For example, in the field ofdocking, a refreshing rate of 5 Hz may be adequate. In time-criticalfields, such as autonomous vehicles, a higher refreshing rate than 5 Hzmay adequate.

The processing unit 105 may also be configured to adjust thepredetermined sequence to account for optical aberration effects. Forexample, in the arrangement where the beam director 103 includescollimating optics such as an angle magnifier or a fish-eye lens, thefield of view may exhibit barrel distortion, causing the field of viewto warp in its outer portion. The processing unit 105 may be configuredto cause the light source 102 to deliberately omit emitting atwavelengths corresponding to some of the outer pixels to counter suchdistortion.

Alternatively the sequential manner includes a randomised sequence. Theprocessing unit 105 may determine the randomised sequence.

In conjunction with optical self-heterodyne detection, the use of aparticular sequence (whether predetermined or randomised) means thatonly reflected light of a specific wavelength channel at a specificlight receiving window are adequately detected, suppressing light atother wavelength channels, thereby enhancing the security of the system.

As mentioned above, the present disclosure provides arrangements wherethe at least one time-varying attribute is either or both of atime-varying intensity profile and a time-varying frequency deviation.Each of these time-varying attributes and the corresponding detectiontechniques to determine round-trip time, and hence round-trip distance,are described further below.

Time-Varying Intensity Control

In arrangements involving a time-varying intensity profile, theprocessing unit 105 may impart a time-varying intensity profile of theoutgoing light. For example, the processing unit 105 may cause amodulation or time-varying current to be applied to the modulator 204,which in turns imparts a time-varying intensity profile on the outgoinglight from tunable laser 202. FIG. 4B illustrates the intensity overtime over the light transmission and receiving windows 401, 402, 403 and404. The time-varying intensity profile in FIG. 4B is illustrative only.There may be a number of different time-varying intensity profilesimparted on the outgoing light as discussed below:

(i) Periodic Intensity Modulation

In one example, within a light transmission window 401, as illustratedin FIG. 4C, the processing unit 105 causes a current having a DCcomponent and a periodic modulation. The periodic modulation may besinusoidal modulation having a single frequency component. For instance,as illustrated in FIG. 4C, the intensity profile 405 includes a 18-MHztone of a single cycle, which translates to a period of 55.6 ns andrepresents a spatial extent of 16.66 m. Any light reflected by an object(i.e. a reflector) and received by the light receiver 104 is expected toinclude the same or substantially the same tone (ignoring non-idealeffects, such as scattering and absorption) that is phase shiftedcompared to a local copy of intensity profile. The phase shift isproportional to the time required for the light to make a round trip toand from the object. In this instance, every additional π/2 or 90° phaseshift represents a reflector distance of 16.66 m/8=2.08 m. Once thereceived light is detected by, e.g. a photodetector as an electricalsignal, the phase shift may be determined by the processing unit 105 byan electrical self-heterodyne method due to the availability of a localcopy of the periodic modulation applied by the processing unit 105.

In this example, where the intensity profile 405 includes a specificfrequency, the processing unit 105 may perform signal processing on thereceived light to inhibit detection of non-reflected light (e.g. spoofedlight). In one arrangement, any received light is detected and convertedto a digital signal, which is then match-filtered by a locally generatedelectrical signal having the same specific frequency. The matchfiltering is mathematically equivalent to a temporal convolutionoperation. If the received light is not at the specific frequency, theconvolution output is expected to be zero. A zero or low output isitself an inhibition of the detection of any non-reflected light.Alternatively, the processing unit 105 may disallow light detection bythe light receiver 104 based on the zero or low output to inhibit thedetection of any non-reflected light. In another arrangement, to allowfor any Doppler shift due to reflected light off a moving reflectingsurface, any received light after conversion to a digital signal isfirst fast-Fourier-transformed to determine the frequency componentspresent in the received light. By adopting a frequency tolerance set byan expected Doppler shift, the processing unit 105 allows lightdetection by the light receiver 104 based on presence of any frequencycomponents that is within the tolerance.

In another instance, the periodic modulation includes multiple frequencycomponents. As illustrated in FIG. 4D, within a light transmissionwindow 401, the intensity profile 406 includes a 18-MHz and 19-MHzdual-tone, resulting in an envelope 407 or beat tone at 1 MHz, whichtranslates to an envelope period of 1 μs and represents a spatial extentof 300 m. Any light reflected by an object (i.e. a reflector) andreceived by the light receiver 104 is expected to include the same orsubstantially the same beat tone (ignoring non-ideal effects, such asscattering and absorption) that is phase shifted or delayed compared toa local copy of intensity profile. The phase shift or delay of theenvelope 407 is proportional to the time required for the light to makea round trip to and from the object. In this instance, every additionalπ/2 or 90° phase shift of the envelope represents a reflector distanceof 300 m/8=37.5 m. Once the received light is detected by, e.g. aphotodetector as an electrical signal, the phase shift may be determinedby the processing unit 105 by an electrical or digital self-heterodynemethod due to the availability of a local copy of the periodicmodulation from the processing unit 105. In addition to determining thephase shift of the envelope, which provides a longer-range measurementof distance, the phase shift of the 18-MHz tone and/or 19-MHz tone maybe determined by the processing unit 105 to provide a shorter-rangemeasurement of distance. In other words, the beat tone is used for acoarse measurement of distance, whereas the individual tone(s) is/areused for a fine measurement of distance.

(ii) Code Modulation

In one example, the processing unit 105 causes a current having a DCcomponent and a pattern or code modulation. The code modulation mayinvolve modulating the intensity profile according to one or more codingsequence. FIG. 4E illustrates one such case of the intensity profile 408of the outgoing light within a light transmission window 401. In thiscase, the intensity varies over time according to a Barker codingsequence of 11100010010, with a logical 1 represented by an increase(+m) in intensity above the DC component and a logical 0 represented bya decrease (−m) in intensity below the DC component. Any light reflectedby an object (i.e. a reflector) and received by the light receiver 104is expected to include the same or substantially the same codingsequence (ignoring non-ideal effects, such as scattering and absorption)that is delayed compared to a local copy of the intensity profile. Thedelay is proportional to the time required for the light to make a roundtrip to and from the object. In this case, once the received light isdetected by, e.g. a photodetector as an electrical signal, theprocessing unit 105 may be configured to perform an autocorrelation ofthe detected signal with a signal generated with the coding sequence,which is known locally to the processing unit 105. The autocorrelationdelay at which a peak autocorrelation signal occurs corresponds to thedistance of the object. For instance, for every additional 10 ns ofautocorrelation delay required to attain a maximum autocorrelationsignal represents an object distance of 1.5 m. An advantage of usingcode modulation with autocorrelation is that the autocorrelation signalas a function of delay typically includes multiple peaks (i.e. localmaxima) at equal delays from either side of the maximum peak (i.e. atdelays −τ₃, −τ₂, −τ₁, 0, +τ₁, +τ₂, +τ₃). The multiple peaks allow moreaccurate determination of the delay at which the maximum peak occurs.Further, the use of code modulation enhances the security of the system.An autocorrelation performed with a sequence that is not the same as thelocally known sequence results in a noisy autocorrelation signal.

It has been suggested that use of Barker code sequences enhances theaccuracy of autocorrelation. However, there are only a limited number ofknown Barker code sequences, and they are of a limited bit length. Toaddress this limitation, another example relies on a combination offast-varying Barker code and a slowly-varying Barker code. Inparticular, as illustrated by FIG. 4F, the processing unit 105 may applythe fast-varying Barker code (with intensity +m and 0 representinglogical 1 and 0 respectively) on top of a slowly-varying Barker code(with additional intensity +m and −m representing logical 1 and 0respectively) to the intensity profile 409 of the outgoing light.

The coding sequence is adjustable for avoidance of interference withanother spatial mapping system. In some configurations, the codingsequence may be randomised. The code may be randomised once, for exampleupon initial start-up of the system or upon factory reset, or may bere-randomised after a certain time has elapsed, for example at regularintervals.

The duration of the transmission and receiving window may also be usedto govern the range of the spatial profiling system. If reflected lightat wavelength λ₁ is received outside the light receiving window 402, itmay not be able to be detected, since the system is either a lighttransmission window, in which the processing unit 105 may be configuredto ignore any light detected by the light receiver 104, or in a lightreceiving window of a different wavelength, leading to a suppresseddetection of wavelength λ₁ if optical self-heterodyne detection is used.

(iii) Aperiodic Intensity Modulation

In one example, the time-varying intensity profile of the outgoing lightmay include aperiodic intensity modulation. In this example, theprocessing unit 105 may cause a current having a DC component andaperiodic modulation to be applied to the light source 102. Theaperiodic modulation may be a chirped sinusoidal modulation. The chirprate may be predetermined, for example, increasing or decreasing infrequency. In one case, the chirp may range between 10 MHz and 100 MHz.For instance, the time-varying intensity profile can be modulated at 10MHz at the start of the light transmission window 401, and modulated at100 MHz at the end of the light transmission window 401, with theintensity modulation gradually increasing from 10 to 100 MHz (ordecreasing from 100 MHz to 10 MHz) during the light transmission window401. The chirp rate may be linear or non-linear.

Alternatively or additionally, the chirp may be changed. For example,the chirp may include intensity modulation starting at 10 MHz andincreased towards 100 MHz for a first time period, and then changed tomodulation starting at 20 MHz and increased towards 200 MHz for a secondtime period after the first time period. Further, the change in thechirp may be predetermined or randomised to inhibit detection ofunintended reflected light (e.g. spoofed light) to increase security.

Any light so aperiodically modulated and reflected by an object (i.e. areflector) and received by the light receiver 104 is expected to includethe same or substantially the same aperiodic modulation (ignoringnon-ideal effects, such as scattering and absorption) that is delayedcompared to a local copy of the intensity profile. The delay isproportional to the time required for the light to make a round trip toand from the object. In this case, once the received light is detectedby, e.g. a photodetector as an electrical signal, the processing unit105 may be configured to perform an electrical or digital heterodynedetection due to the availability of a local copy of the aperiodicmodulation from the processing unit 105. The output of the electrical ordigital heterodyne detection is the difference in modulation frequencybetween the local and the reflected light due to the chirp. With apredetermined or otherwise known chirp rate r, the processing unit 105may be configured to determine the delay based on the output of theelectrical or digital heterodyne detection.

For instance, if the delay between the local and the reflected lightcorresponds to half the transmission window 401 lasting for 1 μs, and ifthe chirp rate is linear from 10 to 100 MHz (i.e. 90 MHz per 1 μs), theelectrical or digital heterodyne detection will produce an outputincluding a 45 MHz difference in modulation frequency between the localand reflected light (based on 10 MHz and 55 MHz at the start and themiddle of the transmission window 401). The processing unit 105 maydetermine based on the 45 MHz difference in modulation frequency fromthe output of the electrical or digital heterodyne detection that thedelay equals 45 MHz/90 MHz×1 μs=0.50 μs, corresponding to a distance tothe target equal to (c×0.5 μs)/2=74.95 m. For a given chirp rate, alarger difference in modulation frequency represents a larger delay anddistance to the target.

Time-Varying Frequency Deviation Control

In arrangements involving a time-varying frequency deviation, theprocessing unit 105 may impart the outgoing light at one or morewavelength channels each with a respective time-varying frequencydeviation f_(d) (t). In these arrangements, the light receiver 104includes an optical self-heterodyne detector, which produces anelectrical signal responsive to the difference in optical frequency (orwavelength) between the received light and the local light. Thiselectrical signal is referred to as the mixed signal below.

FIGS. 5A and 5B illustrate a comparison between arrangements with andwithout such a time-varying frequency deviation. FIG. 5A illustrates anexample where the light source 102 is caused to change its wavelengthchannel in the following sequence: λ₁, λ₂, λ₃, and λ₄ (corresponding tooptical frequency c/λ₁, c/λ₂, c/λ₃, and c/λ₄ where λ_(k) is the centrewavelength of k-th wavelength channel) over time slots 501, 502, 503 and504 without any time-varying frequency deviation. Each time slotsrelates to the transmission and detection of light at the respectivewavelength channel. In contrast, FIG. 5B illustrates an example wherethe light source 102 is caused to change its wavelength channel in thesame sequence over the time slots, but each with a time-varyingfrequency deviation 505. In the example represented by FIG. 5B, allwavelength channels are imparted with the same time-varying frequencydeviation 505. In other examples, the wavelength channels may beimparted with different time-varying frequency deviations. In yet otherexamples, some of the wavelength channels may be imparted with notime-varying frequency deviation. In the example represented by FIG. 5B,the wavelength channels are in a consecutive sequence. In otherexamples, the wavelength channels may be in another predeterminedsequence, such as a non-consecutive sequence, or a randomised sequence.Within each time slot, the optical frequency deviates within itsrespective wavelength channel over time. The frequency deviation may bechanged (increased and/or decreased) linearly at a rate R determined orotherwise known by the processing unit 105. The time-varying frequencydeviation may be in the form of a triangular waveform (e.g. one or moreincreasing and decreasing linear ramps, as shown in FIG. 5B), or asawtooth waveform (e.g. one or more increasing linear ramp followed by asudden decrease of frequency deviation, not shown).

The processing unit 105 may be configured to determine the distance of atarget based on reflected light having the same or substantially thesame time-varying frequency deviation. FIG. 6A illustrates the opticalfrequency of the local light 601 and the received light 602 (top) andthe frequency difference Δf 603 (bottom) over time. Since the frequencydeviation is constantly changing, any reflected light 602 will lagbehind in frequency deviation from the local light 601 by the round-triptime Δt, as illustrated in FIG. 6A. In case of the frequency deviationvarying according to a sawtooth waveform, the frequency difference 603attains a maximum value Δf_(max) in between momentary drops to zerofrequency difference varies over time. Moreover, the further round-tripdistance the reflected light has to travel, the large the round-triptime Δt is, and the larger the frequency difference Δf between thereceived light and the local light is. As mentioned above, the opticalself-heterodyne detector of the light receiver 104 mixes the receivedlight and the local light and produces an electrical signal oscillatingat the frequency difference Δf. The frequency difference Δf is likely inthe radio frequency (RF) region. In the example mentioned earlier, wherethe frequency difference Δf is varied between +/−0.5 GHz, Δf is at most1.0 GHz. Because the frequency deviation changes linearly in a knownrate R, the mixed signal will oscillate at a frequency proportional tothe round-trip distance. Accordingly, the processing unit 105 may beconfigured to determine distance based on a frequency measurement 603 ofthe mixed signal. In particular, the round-trip time Δt is given by:Δt=Δf _(max) /R,  (1)the round-trip distance d_(round-trip) is given by:d _(round-trip) =c×Δt,  (2)and the distance of the target d_(target) is given by half theround-trip distance:d _(target)=(c×Δt)/2,  (3)

Where the target is moving, a Doppler shift in the optical frequency ofthe returned light occurs, where the Doppler shift is based on the speedv of the target. In this case, the processing unit 105 may be configuredto determine the speed and the distance of a target based on reflectedlight having the same or substantially the same time-varying frequencydeviation. FIG. 6B illustrates the optical frequency of the local light601 and the received light 604 (top) and the frequency difference Δf 605(bottom) over time. In case of the frequency deviation varying accordingto a sawtooth waveform, the frequency difference 603 alternates betweenan upper value Δf_(upper) and a lower value Δf_(lower) in betweenmomentary drops to zero frequency difference over time. The processingunit 105 may be configured to determine the target's distance as in thecase where the target is not moving, but replacing Δf_(max) by the meanof Δf_(upper) and Δf_(lower). In addition, the processing unit 105 maybe configured to determine the target's speed v by.

$\begin{matrix}{v = \frac{\left( {f_{upper} - f_{lower}} \right)\lambda}{2\cos\theta}} & (4)\end{matrix}$

where λ is the instantaneous wavelength, and θ is the angle between thetarget velocity vector and the beam direction of the outgoing light.

It should be noted that Equations (1)-(4) are also applicable todetermining the delay (hence target distance) and velocity of a targetwhere the outgoing light includes a time-varying intensity profile inthe form of aperiodic intensity modulation, where the aperiodicintensity modulation includes a linear chirp varying in a sawtoothpattern akin to the top diagram of FIG. 6A. In this instance, theassociated output of the electrical or digital heterodyne detectionresembles the bottom graph of FIG. 6A, with the “optical frequency” nowdenoting the frequency of the intensity modulation (e.g. varying between10 MHz and 100 MHz), Δf now denoting the difference in frequency ofintensity modulation between the local and reflected light, and R nowdenoting the chirp rate.

In this example, where the frequency deviation includes a specificfrequency chirp characteristic (e.g. the known rate R), the processingunit 105 may perform signal processing on the received light to inhibitdetection of non-reflected light (e.g. spoofed light). In onearrangement, the processing unit 105 is configured to determine whetherthe frequency difference 603 remains relatively constant at Δf_(max) (orremaining relatively constant at Δf_(upper) and Δf_(lower) if a certainDoppler shift is to be allowed) for the approximate duration of theplateaus at Δf_(max) represented in FIG. 6A (or the upper and lowerplateaus at Δf_(upper) and Δf_(lower) represented in FIG. 6B). If thedetermination is negative, the processing unit 105 may disallow lightdetection by the light receiver 104 based on the negative determinationto inhibit the detection of any non-reflected light. In anotherarrangement, to allow for any Doppler shift due to reflected light off amoving reflecting surface, the processing unit 105 is configured todetermine whether the frequency difference 603 remains at Δf_(upper) andΔf_(lower) for the approximate duration of the upper and lower plateausat Δf_(upper) and Δf_(lower) represented in FIG. 6B. If thedetermination is negative, the processing unit 105 may disallow lightdetection by the light receiver 104 based on the negative determinationto inhibit the detection of any non-reflected light.

Temperature Monitoring

The wavelength stability of laser diodes is temperature-dependent. Insome arrangements, the laser diode (or its packaging or mounting)includes an etalon module, which facilitates tracking changes inwavelength due to ambient temperature changes. The etalon module mayinclude an etalon, which consists of two partially reflective andsubstantially parallel interfaces, optically coupled to a lightintensity detector. The light intensity detector generates an electricalsignal based on the intensity of light transmitted or reflected by theetalon. It has been known that the reflectivity and transmissivity of anetalon are highly sensitive to temperature changes (see, for example,Appl Opt. 1971 Sep. 1; 10(9):2065-9). The intensity of the lightdetected by the light intensity detector therefore provides anindication of the temperature changes in or near the etalon. Theprocessing unit 105 may be configured to receive temperature-relatedinformation from the etalon module. Based on the temperature-relatedinformation, the processing unit 105 may provide a feedback signal tothe light source 102 to wavelength-compensation due to any temperaturedrift. This feedback mechanism relaxes the requirements of the lightsource 102 by, for example, eliminating the need for an activetemperature control.

Environmental-Effects Monitoring

In an arrangement where the beam director 103 is remote from the centralunit (such as that in FIG. 1C), it may also be beneficial to obtainenvironment-related information from the remote beam director tocharacterise the environment-related effects which the remote beamdirector is subject to. For those arrangements where the beam director103 includes two spatially dispersive elements for spatially dispersinglight into two substantially orthogonal directions, the beam director103 may further include in one of the two spatially dispersive elementsa cavity for obtaining environment-related information. Like an etalon,the cavity's reflectivity and transmissivity can be highly sensitive totemperature or other physical effects, such as stress.

For example, referring to FIG. 3B, the cavity may be formed by partiallyreflected coatings in a region of the second spatially dispersiveelement 303 to which light emitted at wavelength from λ₁₁ to λ₂₀ (i.e.the second row of pixels) from the light source 102 would be directed.In this example, the wavelengths λ₁₁ to λ₂₀ are designated formonitoring environmental-related effects. When environmental-relatedinformation, such as temperature or stress information, is desired at aparticular time, the processing unit 105 may be configured to cause thelight source 102 to emit any one of the wavelengths λ₁₁ to λ₂₀. Suchemitted light when directed by the beam director 103 reaches the cavity(instead of the environment). The intensity of light reflected by thecavity (instead of the environment) and subsequently received by thelight receiver 104 provides environmental-related information at or nearthe cavity.

For example, in an automotive application, the system is required tooperate in an extended range of temperatures (e.g. −40 to +60 degreeCelsius), where passive components in the beam directors may also changeproperties with temperature. Slight mismatches in the thermal expansioncoefficient of different optical materials or glues may introduce stressand changes in the passive optics leading to undesirable effects such asoptical misalignment. Since these temperature-related effects will bedifferent for different parts, there may be a need to characterise themat the time of manufacture to calibrate these effects away duringoperation. If this calibration is performed over temperature, obtainingtemperature information at time of operation will allow the system to betemperature-compensated based on the calibration.

Now that arrangements of the present disclosure are described, it shouldbe apparent to the skilled person in the art that the describedarrangements have the following advantages:

-   -   The use of a wavelength-dependent beam director directs the        outgoing light in a direction based on wavelength, requiring no        moving parts and with no or little inertia to improve the speed        of beam re-direction.    -   In arrangements where the intensity profile is varied over time,        compared with techniques measuring a time delay of optical        pulses, which may require the use of photodetectors of fast        response time (of the order of 1 ns) due to the use of short        optical pulses for improved time resolution, the use of periodic        modulation or code modulation (together with phase-shift or        autocorrelation detection method) reduces the response time        requirements on the light receiver to achieve a similar time        resolution.    -   In arrangements where the frequency deviation is varied over        time, the, the same wavelength control can be used for frequency        deviation and beam direction.    -   The security or the ability to counter “spoofing” is facilitated        by any one or more of the following:        -   With optical self-heterodyne detection, only light of a            specific wavelength received at a specific time (e.g. light            receiving window) may be adequately detected. The sequence            of wavelength in a specific order may also be used to            enhance security.        -   With modulation, such as periodic or code modulation, only            light whose intensity is varied in a specific fashion (such            as at a specific frequency or modulated with a specific            coding sequence) may be adequately detected.        -   For beam director(s) having spatially dispersive optics,            only light received at from particular direction by the beam            director(s) may be adequately routed to the light receiver            and thus be adequately detected.        -   Where the described system is used for line-of-sight            communication (e.g. free-space optical or microwave)            alignment purposes, the spatial map of the environment may            be used for aligning the communication beam (e.g. the            optical beam or microwave beam) towards a transceiver. For            instance, the transceiver may be marked by a recognisable 3D            shape (e.g. donut-shaped). Once the recognisable 3D shape is            recognised (e.g. by way of 3D shape recognition software) in            the spatial profile of the environment, a line-of-sight            communication system may be configured to point to the            direction of the recognised transceiver for line-of-sight            communication. In the case of free-space optical            communication, the very light from light source 102 directed            as the outgoing light by beam director 103 may be used for            the light source for the free-space optical communication            once alignment is achieved. Similarly, the very light            received by the light receiver 104 directed as the incoming            light by beam director 103 may be used for the light            received for the free-space optical communication once            alignment is achieved.

It will be understood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features mentioned or evident from the text or drawings.For example, modulator means other than SOA or a Mach Zehnder modulatormay well be suitable. All of these different combinations constitutevarious alternative aspects of the invention.

What is claimed is:
 1. A spatial profiling system including: a lightsource configured to provide outgoing light at a plurality of wavelengthchannels, including first outgoing light having at least one timevarying attribute at a first wavelength channel and to provide secondoutgoing light having at least one time varying attribute at a secondwavelength channel, different to the first wavelength channel, the atleast one time varying attribute including at least one of: (a) anintensity profile modulated according to one or more coding sequencesand (b) time-varying frequency deviation; a beam director configured tospatially direct the outgoing light along a spatial direction into anenvironment having a spatial profile, wherein the spatial direction isbased on wavelength and includes directing the first outgoing light in afirst direction and directing the second outgoing light in a seconddirection, different to the first direction; a light receiver configuredto receive at least part of the first outgoing light reflected by theenvironment and to receive at least part of the second outgoing lightreflected by the environment; and a processing unit configured todetermine at least one characteristic associated with the at least onetime varying attribute of the received reflected light for estimation ofthe spatial profile of the environment associated with the first andsecond directions.
 2. The spatial profiling system of claim 1, whereinthe light receiver is configured to inhibit detection of non-reflectedlight based on a difference in wavelength or modulation between theoutgoing light and the non-reflected light.
 3. The spatial profilingsystem of claim 1, wherein the at least one characteristic is indicativeof a time delay of the received reflected light.
 4. The spatialprofiling system of claim 3, wherein the at least one time varyingattribute includes said intensity profile modulated according to one ormore coding sequences and wherein the processing unit is configured todetermine the time delay of the received reflected light based oncorrelation between signals detected in the received reflected light andsignals representative of the one or more coding sequences.
 5. Thespatial profiling system of claim 4, wherein the correlation includesone or more peak correlation values occurring at respective one or morecorrelation delays.
 6. The spatial profiling system of claim 5, whereinthe time delay of the received reflected light is determined based onthe one or more correlation delays.
 7. The spatial profiling system ofclaim 1, wherein the at least one time varying attribute includes saidtime-varying frequency deviation and wherein the time-varying frequencydeviation includes a linear frequency increase, decrease or both overtime.
 8. The spatial profiling system of claim 7, wherein the processingunit is configured to determine a time delay of the received reflectedlight based on a difference in an optical frequency between the receivedreflected light and either or both of the first outgoing light and thesecond outgoing light.
 9. The spatial profiling system of claim 7,wherein the processing unit is configured to further determine a Dopplershift in an optical frequency of the received reflected light.
 10. Thespatial profiling system of claim 9, wherein the Doppler shift isdetermined based on differences in the optical frequency between thereceived reflected light and either or both of the first outgoing lightand the second outgoing light.
 11. A method of spatial profiling, themethod including: providing, by a light source, outgoing light at aplurality of wavelength channels, including first outgoing light havingat least one time varying attribute at a first wavelength channel and toprovide second outgoing light having at least one time varying attributeat a second wavelength channel, different to the first wavelengthchannel, the at least one time varying attribute including at least oneof: (a) an intensity profile modulated according to one or more codingsequences and (b) time-varying frequency deviation; spatially directing,by a beam director, the outgoing light along a spatial direction into anenvironment having a spatial profile, wherein the spatial direction isbased on wavelength and includes directing the first outgoing light in afirst direction and directing the second outgoing light in a seconddirection, different to the first direction; receiving, by a lightreceiver, at least part of the first outgoing light reflected by theenvironment and to receive at least part of the second outgoing lightreflected by the environment; and determining, by a processing unit, atleast one characteristic associated with the at least one time varyingattribute of the received reflected light for estimation of the spatialprofile of the environment associated with the first and seconddirections.
 12. The method of claim 11, further including inhibitingdetection of non-reflected light based on a difference in wavelength ormodulation between the outgoing light and the non-reflected light. 13.The method of claim 11, wherein the at least one characteristic isindicative of a time delay of the received reflected light.
 14. Themethod of claim 13, wherein the at least one time varying attributeincludes said intensity profile modulated according to one or morecoding sequences and wherein the method further includes determining, bythe processing unit, the time delay of the received reflected lightbased on correlation between signals detected in the received reflectedlight and signals representative of the one or more coding sequences.15. The method of claim 14, wherein the correlation includes one or morepeak correlation values occurring at respective one or more correlationdelays.
 16. The method of claim 15, wherein the time delay of thereceived reflected light is determined based on the one or morecorrelation delays.
 17. The method of claim 11, wherein the at least onetime varying attribute includes said time-varying frequency deviationand wherein the time-varying frequency deviation includes a linearfrequency increase, decrease or both over time.
 18. The method of claim17, further including determining, by the processing unit, a time delayof the received reflected light based on a difference in an opticalfrequency between the received reflected light and either or both of thefirst outgoing light and the second outgoing light.
 19. The method ofclaim 17, further including determining, by the processing unit, aDoppler shift in an optical frequency of the received reflected light.20. The method of claim 19, wherein the Doppler shift is determinedbased on differences in the optical frequency between the receivedreflected light and either or both of the first outgoing light and thesecond outgoing light.